A VVT (Variable Valve Timing) has conventionally been known that changes the phase (crank angle) in (at) which an intake valve or an exhaust valve is opened/closed, according to an operating condition. Generally, in the variable valve timing apparatus, the phase is changed by rotating a camshaft, which opens/closes the intake valve or exhaust valve, relative to a sprocket or the like. The camshaft is rotated by an actuator such as a hydraulic or electric motor.
Such a variable valve timing is operated while the vehicle is driven, and sometimes it is operated even after an engine-stop instruction is issued by an off-operation of an ignition key, to change the valve timing (cam shaft phase). Specifically, when the valve timing at the time point when the engine-stop is instructed is different from the valve phase suitable for starting the engine next time, the valve timing is changed by the variable valve timing apparatus, to be ready for the next start of engine operation.
For example, Patent Document 1 (Japanese Patent Laying-Open No. 2004-156508) discloses a valve timing controller that changes the valve timing to attain an angular position suitable for the start of engine operation next time, by applying a current for a prescribed time period to a hysteresis brake as an electromagnetic actuator, after the ignition key is turned off. Patent Document 2 (Japanese Patent Laying-Open No. 2005-291200) discloses a structure in which timing of opening/closing an intake valve or an exhaust valve at the start of an engine is set to a start timing of an advanced angle side rather than the timing corresponding to the most retarded angle, and the variable valve timing is controlled such that the opening/closing timing when the engine is stopped is set to correspond to the start timing.
Further, Patent Documents 3 and 4 (Japanese Patent Laying-Open Nos. 2005-264864 and 2000-080939) disclose controllers that ensure good starting characteristic even when the actual valve timing is off from an appropriate start timing, by correcting an amount of fuel injection (supply amount) at the start of the engine in accordance with the actual valve timing.
In the valve timing controller disclosed in Patent Document 1, however, the valve timing is controlled such that, in response to turning-off of the ignition key, a process of stopping the engine is executed immediately, and by applying power to the hysteresis brake for a prescribed time period starting from the time of turning-off, the valve timing comes to be the start timing. Therefore, in a variable valve timing apparatus in which it is difficult to change the valve timing after the engine is stopped, the amount of possible change of the valve timing in the engine stop operation is limited.
Similarly, in the valve timing controller disclosed in Patent Document 2, a control structure is disclosed in which the valve timing is controlled with the start timing used as a target value when the engine stop operation is done. This reference, however, is silent about any structure to ensure sufficient amount of change in the valve timing. The same applies to Patent Documents 3 and 4.